Loline alkaloids (LA; saturated 1-aminopyrrolizidine alkaloids with an ether bridge, FIG. 1), are produced in a number of associations of grasses with endophytes of the genus Epichloë and their asexual descendants, Neotyphodium spp. In addition, LA are reported from the plants Adenocarpus spp. and Argyreia mollis of the families Fabaceae and Convolvulaceae, respectively. LA produced in grass-endophyte symbioses have strong insecticidal and feeding-deterrent properties (Riedell,et al., 1999, J Entomol. Sci. 26: 122–129; Wilkinson et al., 2000, Mol. Plant-Microbe Interact. 13: 1027–1033). Moreover, grasses infected by LA-producing endophytes, such as Neotyphodium coenophialum and N. uncinatum, have greater tolerance to drought conditions (Arechavaleta et al., 1989, Agron. J 81: 83–90; Bacon, 1993, Agric. Ecos. Environ. 44: 123–141 ) than grasses infected by closely related endophytes, such as N. lolii, that do not produce LA (Barker et al., 1997, Agric. Ecos. Environ. 44: 123–141; Cheplick et al., 2000, Mycol. Res. 97: 1083–1092.). Growth suppression (allelopathy) of neighboring plants by meadow fescue (Lolium pratense) infected with N. uncinatum may indicate a potential for additional beneficial roles of these alkaloids in grass plant competitiveness and persistence.
LA can accumulate to extremely high levels in grass tissues, occasionally reaching more than 2% of the plant's dry mass (Craven et al., 2001, Sydowia 53: 44–73). These quantities far exceed the biomass of the fungus and the amounts of other alkaloids, such as ergot alkaloids, indole-diterpenoids, and peramine, also produced in some of the endophyte-grass symbiota. However, despite their exceptional levels in the grass and importance of LA in grass survival, little is known about LA biosynthesis. This is in contrast to some of the other endophyte-associated alkaloids, such as ergopeptines and indole-diterpenoids, for which much of the biosynthetic pathways have been elucidated and key enzymes identified.
It was previously unknown whether LA are of fungal or plant origin, or produced by both symbiotic partners together, but a recent study has established that N. uncinatum can produce LA in axenic culture (Blankenship et al., 2001, Phytochemistry 58: 395–401). This finding presents opportunities to identify genes involved in LA biosynthesis. Knowledge of the LA biosynthesis genes would allow more detailed studies on the roles of LA in plant persistence, in particular on possible contributions to abiotic stress tolerance, as well as the cloning and use of these genes to generate genetically engineered plants.